The present invention relates generally to hydraulic couplings for use in motor vehicle driveline applications. More specifically, the hydraulic coupling includes a hydraulic pump, a transfer clutch coupled between a pair of rotary members, and a fluid distribution system including a control valve assembly operable for controlling actuation of the transfer clutch.
Hydraulic couplings are used in a variety of motor vehicle driveline applications for limiting slip and transferring drive torque between a pair of rotary members. In all-wheel drive applications, hydraulic couplings have been used to automatically control the transfer of drive torque from a driven member to a non-driven member in response to speed differentiation therebetween. In limited slip applications, such as used in association with a differential in an axle assembly, full-time transfer case, or transaxle, hydraulic couplings have been used to limit slip and bias the torque split between two rotary members. Examples of known hydraulic couplings which are adaptable for such driveline applications include viscous couplings, geared traction units, and passively and electronically-controlled hydraulically-actuated friction clutches generally similar to those shown and described in U.S. Pat. Nos. 5,148,900, 5,358,454, 5,649,459, 5,704,863 and 5,779,013.
It is an object of the present invention to provide a hydraulic coupling for use in motor vehicle driveline applications that is operable for limiting speed differentiation and transferring drive torque between two rotary members.
In accordance with this object, the hydraulic coupling includes a multi-plate clutch assembly operably connecting two relatively rotatable members, and an actuator assembly for actuating the clutch assembly in response to speed differentiation between the two rotary members. The actuator assembly includes a hydraulic pump, a piston disposed in a piston chamber, and a fluid distribution system including a first flow path for supplying hydraulic fluid from a sump to the hydraulic pump and a second flow path for supplying hydraulic fluid from the hydraulic pump to the piston chamber. Hydraulic pressure in the piston chamber controls the magnitude of the clutch engagement force exerted by the piston on the clutch assembly. The fluid distribution system further includes a third flow path between the piston chamber and a clutch chamber. A control valve assembly is located in the third flow path and provides a flow control function for regulating the fluid pressure in the piston chamber and supplying fluid to the clutch chamber for cooling the clutch assembly.
As an additional feature of the hydraulic coupling, the flow control function provided by the control valve assembly is thermally compensating for accommodating viscosity changes due to heating of the hydraulic fluid. Furthermore, the flow control function is speed compensating for varying the engagement characteristics of the clutch assembly as a function of vehicle speed.
As a further feature of the hydraulic coupling, the control valve assembly provides a pressure relief function for setting a maximum pressure within the piston chamber.
As still a further feature of the hydraulic coupling, the control valve assembly provides a thermal unload function for releasing the pressure within the piston chamber when the fluid temperature exceeds a predetermined temperature value.
As another feature, the hydraulic coupling can be used in an all wheel drive system for transferring power to the secondary driveline.
As still a further feature of the hydraulic coupling, the control valve assembly is located within the piston chamber, in close proximity to the clutch pack where a majority of heat is generated, thus providing a more responsive system.